Saturday, June 16, 2012

In a comment on the post below, a bunny who wishes to remain Unknown points to a Jennifer Francis's work on how global climate has been changed by climate change and specifically ice melt in the Arctic

which is summarized as

If the theory is correct, that Arctic amplification reduced ice pack
alters the jet stream patterns, leading to prolonged weather patterns,
then we have entered a new meteorological system. Then shifted
probability curves (based on the old meteorology) don't really make
sense. The new meteorology we have created could have a very different
probability curve for prolonged heat waves (as well as droughts, cold
spells, extreme and prolonged flooding events, major snowstorms) in the
NH than the prior meteorology.

but in passing makes an important point that Eli has repeated several times, most often over at Open Mind. One can too easily fall into the trap of only looking at the statistical properties of some occurrence, it is even more important to understand the physical origins, as a matter of fact the later in IEHO is more important, sometimes you have to wait a bit on the statistics, but the physics (and chemistry) is basic.

Another approach to studying these events tries to identify whether the
meteorology of the earth has changed. Prolonged weather patterns
produces a heat wave, instead of a hot week. And prolonged weather
patterns depend on the positioning of the jet stream. The direct cause
of all three events in your post was a stalled jet stream (a blocking
pattern in the jet stream).

Thanks for pulling this up out of the comments and for anon's comment.

This intersection of climate and weather is a very interesting arena because people don't live in 30 year averages - and as far as I know, this kind of detail is not caught in the current generation of AOGCMs.

Yet, it seems like this is precisely the kind of thing that can drive western US snowpack and eastern US snowstorms. And I wonder if the increased amplitude and slower phase of the Rossby waves makes a play in the recent heat wave in Russia and extended rain in Pakistan.

In a previous post you pointed out that many people's opinion of climate science are driven by their personal experience of the degree of match between local weather and what they believe to be GCM predictions. When weather seems warmer their belief goes up. When weather seems colder and/or snowier, it goes down.

The whole 'weighted dice' narrative is an attempt to get beyond that, to help align climate predictions to experienced weather. But it is a strained relationship since, AFAIK, GCMs are not producing the natural range of variability that can be considered weather-like. And, AFAIK, aren't showing anything like this arctic impact on the Rossby waves.

Current consensus on global climate change predicts warming trends driven by anthropogenic forcing, with maximum temperature changes projected in the Northern Hemisphere (NH) high latitudes during winter. Yet, global temperature trends show little warming over the most recent decade or so. For longer time periods appropriate to the assessment of trends, however,global temperatures have experienced significant warming for all seasons except winter, when cooling trends exist instead across large stretches of eastern North America and northern Eurasia. Hence, the most recent lapse in global warming is a seasonal phenomenon, prevalent only in boreal winter. Additionally, we show that the largest regional contributor to global temperature trends over the past two decades is land surface temperature in the NH extratropics. Therefore, proposed mechanisms explaining the fluctuations in global annual temperature trends 13 should address this apparent seasonal asymmetry.

Their Fig. 3 illustrates the point very clearly. Interesting stuff. I did *not* know that DJF temperatures in the NH extratropics were doing this.

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Eli Rabett

Eli Rabett is a not quite failed professorial techno-bunny, a chair election from retirement, at a wanna be research university that has a lot to be proud of but has swallowed the Kool-Aid. The students are naive but great and the administrators vary day-to-day between homicidal and delusional. His colleagues are smart, but they have a curious inability to see the holes that they dig for themselves. Prof. Rabett is thankful that they occasionally heed his pointing out the implications of the various enthusiasms that rattle around the department and school. Ms. Rabett is thankful that Prof. Rabett occasionally heeds her pointing out that he is nuts.